The Food and Drug Administration (FDA) has recently considered setting standards and testing procedures for measuring drug release from topical creams and ointments. The proposed testing procedures would be analogous to current procedures that are used to test tablets and capsules for dissolution specifications.
The accepted apparatus employed and expected to be recommended by the FDA is the Franz cell (FIG. 1). In the Franz cell test aliquots are drawn manually at intervals from the side arm to determine the amount of drug release.
One proposed modification to the Franz cell is a device which automates the transfer of test aliquots from the cell. This device utilizes a six syringe pump to displace receptor media out of the cell and into the collection vial(s). While this device appears to be workable, it has several limitations and drawbacks. Because the device functions by displacing the receptor media in the cell it operates under pressure. Since previous studies of drug release from topical creams and ointments has involved testing under atmospheric pressures, comparisons between all previous work may not be possible when using a system that operates under pressure. In addition to providing results which are incompatible with all previous work, the use of a pressure operated system can cause serious reliability problems since any leaks will cause inconsistent collection of the test aliquots.
Furthermore, the use of syringe pumps involves minimum aliquots of about 1.2 ml due to the volume of fluid required to flush the delivery lines with the succeeding receptor media before an aliquot can be collected. This limitation reduces the concentration of the drug in the cell and impairs the delectability of very slightly soluble drugs.
An alternative approach is to provide a pump that is suitable for pumping the transfer fluid from the cell, through the collection head and back to the cell thus allowing the delivery lines to be to be flushed without and reducing the concentration of the drug in the cell. While peristaltic pumps have been used for this purpose, they have several operational drawbacks. For example, the precise volume delivered can be difficult to adjust when using a peristaltic pump. In addition, there are many drugs that are known to absorb on various tubing materials used in peristaltic pumps.
The present invention provides a pump which overcomes the disadvantages of the prior art.